The basic aim of this work is to study the relationship of oxygen supply and demand on a regional basis in the heart and other organs under control and stressful conditions. To this end we have developed a new and highly accurate microspectrophotometric method for determination of the oxygen saturation in small arteries and veins of a quick frozen tissues. By combining these measurements with a regional flow determination with radioactive microspheres, regional oxygen consumption can be calculated for the first time quantitatively. Such measurements are now proceeding in the heart. Most measurements will be performed on anesthetized open chest dogs and minipigs. The effects graded flow reduction on regional myocardial oxygen consumption will be studied. The effects of increasing heart work through atrial pacing, valvular or supravalvular stenosis on the relations of myocardial oxygen supply to demand will be determined. Studies will also be conducted of agents that are of proposed utility in the treatment of infarction, coronary artery disease and angina pectoris. Determination of the oxygen supply-demand relation in the brains of conscious cats under different conditions will be determined on a regional basis. Measurement of oxygen saturation will be obtained from the blood vessels of the carotid bodies of anesthetized cats to determine if areas of differing saturation exist in euoxic or hypoxic conditions. All of these studies will allow quantitative measurements to be obtained of regional oxygen consumption in different organs and under different conditions.